Interpolyelectrolyte complexes formed by DNA and astramol poly(propylene imine) dendrimers

Investigations have been carried out to clarify the binding interactions between two kinds of native DNA: one from salmon sperm (300-500 bp) and another from bacteriophage T4dC (166 kbp) and amine-terminated, diaminobutane core, poly(propylene imine) dendrimers (Astramol) of five generations (G1, G2, G3, G4, and G5). All dendrimers interacting with DNA at an equal concentration of amine and phosphate groups form electroneutral water-insoluble interpolyelectrolyte complexes (IPECs). However, G4 and G5 added to DNA solution in excess form positively charged water-soluble IPECs representing perfect objects to investigate the state of DNA molecules incorporated into IPEC. Using UV spectroscopy and CD spectroscopy combined with ultracentrifugation, it is shown that complexed DNA compacts, revealing a wound double-helical structure. Using fluorescence microscopy, we observed compaction of individual ultrahigh molecular mass DNA interacting with excess of G4 to form water-soluble positively charged IPECs "unimers".